The morphology of cross-linked multi-vesiculated polyester particles described in prior art consist of largely spherical hollow particles with multiple air voids in the dry state. These particles re-absorb water in paints and coatings, are difficult to manufacture and their particle size control is limited to processing variables such as temperature, speed of agitation and process time.
Prior art patent WO 81/01711 for the production of vesiculated beads. In this process, a first emulsion (EMI) is formed in which an aqueous phase having pigment dispersed therein is emulsified in a mixture of an unsaturated polyester and a co-polymerisable monomer as a solution of the polyester in the monomer. This is a water-in-oil-emulsion. EMI is then emulsified at high shear into an aqueous phase to form a water-in-oil-in-water emulsion having the oil phase as globules of polyester/monomer each containing a number of vesicles of the initial aqueous phase. A polymerising initiator is added to initiate crosslinking of the polyester under curing conditions to form the desired vesiculated beads. Shorter chain monomers (C12 and less) which have minimal hydrophobicity, are used.
It is an object of this invention to provide cross-linked polyester particles whose morphology is largely spherical with multiple air voids that hinder the re-entry and re-absorption of water when the cross-linked particles are dry.
It is a further object of the invention to provide a conversion process of the raw materials composition which permits cross-linked particle size and distribution control through process variables such as temperature, rate of agitation and processing time as well through the concentration of modifying co-monomer in the raw material composition and the optimization of the process stage for adding this co-monomer to the said composition.
It is yet a further object of this invention to provide a vesiculated polymer particle which may be used in paint and coatings formulations for the beneficial replacement of titanium dioxide pigments, expensive extenders, emulsion polymers, open time modifiers such as glycols and humectants with simultaneous achievement of improved opacity, whiteness, scrub resistance, water resistance and special faux finish effects.